This invention relates generally to silicon controlled rectifier (SCR) devices and more particularly concerns a high voltage switch that is built laterally in a polysilicon layer deposited above other microelectronic devices.
Devices, such as stacked or cascaded transistors, have been used to turn on extremely high voltages, however structures of this type are inherently long, consume large amounts of silicon and have reliability problems. There has not been a single device that can be used to turn on extremely high voltages for example, voltages of 20,000 volts or more.
Conventional SCRs can be used as specialized switches. One important aspect of designing SCRs is that there is no upward limit on the number of p-n junctions which can be combined to form an SCR device. Increasing the number of p-n junctions in an SCR allows design of a single high voltage device that can be used as a switch.
New processing technologies have led to the development of an ability to build a reasonably good SCR device in layers above that of transistors built within substrate layers of a wafer. Utilizing SCR characteristics to build a single device as a high voltage switch and then building the SCR in the layers above that of conventional transistors has led to the development of a single high voltage switch that does not use the large quantities of area required for conventional high voltage switches.
Accordingly, it is the primary aim of the invention to provide a single high voltage device capable of switching high voltages and not requiring large quantities of silicon area.
Further advantages of the invention will become apparent as the following description proceeds.